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FR4 Sheet — Sizes, Thicknesses, Tolerances & Ordering

FR4 sheet is glass-epoxy thermoset laminate in flat panel form, carrying UL94 V-0 flame-retardant rating and governed by NEMA LI 1 Grade FR-4 and IPC-4101 for PCB-grade variants. Structural FR4 sheet covers thicknesses from 0.031" through 0.500"; heavier stock above 0.500" is classified as FR4 plate. FR4 sheet is stocked by electrical insulation distributors for CNC machining into bus bar spacers, arc barriers, PCB tooling fixtures, and other components requiring the V-0 flame rating that distinguishes FR4 from G10.

At a glance:

  • Thickness range: 0.031" to 0.500" (structural sheet); 0.005"–0.125" (PCB-grade CCL cores)
  • Standard panel sizes: 36" × 48" and 48" × 96" (structural); 18" × 24" and 24" × 36" (PCB CCL)
  • Thickness tolerance: ±10% (NEMA LI 1); ±0.005"–0.010" (IPC-4101 CCL)
  • Color: green (standard); yellow or natural for some unclad grades
  • UL94 rating: V-0 across all standard FR4 sheet grades
  • Grades available: standard Tg (130–140°C), high-Tg (170°C+), halogen-free

Standard FR4 Sheet Thicknesses

The 0.062" thickness is by far the most widely stocked and sourced FR4 sheet thickness, driven by its dominance as the standard PCB laminate. For structural applications where 0.062" provides adequate mechanical strength, sourcing is easiest at this thickness.

Standard Panel Sizes

ApplicationTypical Panel SizesNotes
Structural insulation36" × 48", 48" × 96"Full panel; cut to size available
PCB copper-clad (CCL)18" × 24", 24" × 36"For PCB fabricators; sold as CCL
Small format / prototyping12" × 12", 12" × 24"Cut pieces; common stock sizes

Custom sizes and cut pieces are available from most distributors. FR4 sheet saws cleanly on circular saws with carbide ATB blades; see FR4 machining for cutting guidance.

Thickness Tolerances

Thickness tolerance varies by standard and thickness:

Thickness RangeTolerance (NEMA LI 1)Tolerance (IPC-4101 /24 CCL)
0.005"–0.031"±10%±0.003"–0.005"
0.031"–0.125"±10%±0.005"–0.008"
0.125"–0.500"±10%±0.008"–0.012"

IPC-4101 imposes tighter tolerances than NEMA LI 1 for CCL used in PCB manufacturing because layer-to-layer thickness consistency directly affects controlled-impedance trace design. For structural applications, the ±10% NEMA tolerance is generally adequate.

Materials Available as FR4 Sheet

FR4 sheet is available in several grade variants. Selecting the right one avoids over-specification:

Standard FR4 (Tg 130–140°C) — Broadest availability; lowest cost. Suitable for operating temperatures below 100°C sustained. PCB-grade per IPC-4101 /21 (unclad) or /24 (CCL). The default unless a specific higher-Tg or halogen-free requirement applies.

High-Tg FR4 (Tg 170°C+) — Required for lead-free solder reflow assemblies and high-temperature power electronics. IPC-4101 /41 (unclad) or /42 (CCL). Premium of approximately 20–35% over standard FR4.

Halogen-Free FR4 — Bromine and chlorine content below 900 ppm per IEC 61249-2-21. V-0 via phosphorus-nitrogen FR chemistry. IPC-4101 /99 for high-Tg halogen-free CCL. Appropriate where TBBPA REACH SVHC documentation is a supply chain concern.

For grade selection logic, see FR4 grades.

FR4 Sheet vs G10 Sheet

The most common procurement question for FR4 sheet is whether G10 can be substituted. The answer depends entirely on the application's flame-retardancy requirement:

CriterionFR4 SheetG10 Sheet
UL94 flame ratingV-0None (HB or unrated)
Required for UL 508A listed panelsYesNo
Required for IEC 62368-1 compliant equipmentYesNo
Price premium over G10+10–20%Baseline
Electrical propertiesEssentially identicalEssentially identical
Mechanical propertiesEssentially identicalEssentially identical

If your application is covered by a product safety standard that requires V-0 rated insulation, FR4 sheet is mandatory. If not, G10 sheet is a cost-effective alternative. See the G10 vs FR4 comparison for detailed guidance.

How FR4 Sheet Is Made

FR4 sheet is produced by a multi-step lamination process:

  1. Prepreg manufacturing: E-glass fabric is impregnated with a catalyzed brominated epoxy resin solution and passed through a treater oven, partially curing ("B-staging") the resin to a stable, handleable state
  2. Lay-up: Multiple prepreg plies are stacked to achieve the target laminate thickness; copper foil is added for CCL
  3. Pressing: The stack enters a heated hydraulic press at 175–185°C and 200–300 psi; the resin flows and fully cures ("C-stage") over 60–90 minutes
  4. Post-processing: Pressed panels are cooled under controlled conditions, trimmed, and inspected for thickness, flatness, and surface quality
  5. Testing: Dielectric strength, moisture absorption, and peel strength (for CCL) are tested per IPC-TM-650 or ASTM D229

The number of prepreg plies determines finished thickness: a single ply of 7628 glass style yields approximately 0.0072" per ply; twenty-four plies yield approximately 0.173" before press consolidation (actual thickness slightly thinner due to resin flow and consolidation).

Specifications to Request When Ordering FR4 Sheet

When placing an order for structural FR4 sheet, provide:

  1. Thickness: Nominal in inches or mm; specify ±10% NEMA or tighter if needed
  2. Panel size: Standard or custom cut dimensions
  3. Grade: Standard Tg, high-Tg (specify minimum Tg), or halogen-free
  4. Standard: NEMA LI 1 FR-4 (for structural); IPC-4101 /21 or /24 (for PCB-grade)
  5. Copper clad: Yes/no; if yes, specify copper weight (1/2 oz, 1 oz, 2 oz) and sides (1 or 2)
  6. Documentation: Cert of conformance, UL94 listing documentation, RoHS declaration as required

Order FR4 sheet — standard and high-Tg grades, cut to size

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Frequently asked questions — FR4 FAQ

Other FR4 Reference Guides

FR4 SpecificationsFR4 specifications: IPC-4101 sub-classes, standard sheet sizes, thickness classes, copper-clad vs unclad, and glass styles (1080, 2116, 7628) for PCB and structural use.FR4 TubeFR4 tube: mandrel-wound glass-epoxy tube with UL94 V-0 rating. Standard OD 0.50"–12", used for coil forms, insulating sleeves, and conduit in high-voltage equipment.FR4 RodFR4 rod: mandrel-wound glass-epoxy rod with UL94 V-0 rating. Standard diameters 0.25"–6.0", 36" lengths. Used for standoffs, bushings, and shaft insulators in switchgear.FR4 PlateFR4 plate: 0.500" to 2.0"+ thick glass-epoxy laminate for bus bar supports, switchgear barriers, HV test fixtures, and machined electrical insulation. UL94 V-0.FR4 FDA Food-Grade StatusFR4 is not FDA approved for food contact. Brominated epoxy resin (TBBPA) and uncured epoxy components disqualify all FR4 grades from food-contact and food-processing use.FR4 Dielectric StrengthFR4 dielectric strength: ~500 V/mil perpendicular (ASTM D149), testing methods, factors affecting values, grade comparisons, and IPC-4101 requirements explained.FR4 ApplicationsFR4 applications: PCB substrate, structural electrical insulation, switchgear bus bar spacers, transformer parts, and electronic enclosures where UL94 V-0 is required.FR4 Machining GuideFR4 machining guide: drill speeds, router bits, V-scoring, and tool wear management for glass-fiber epoxy laminate. Covers brominated dust hazards and surface finish.FR4 GradesFR4 grades explained: standard FR4 (Tg 130–140°C), high-Tg FR4 (170°C+), halogen-free FR4, and IPC-4101 sub-classes /21, /24, /41, /99 for PCB and structural use.FR4 FAQFR4 FAQ: answers to common questions about FR4 vs G10, dielectric strength, UL94 rating, high-Tg FR4, machinability, food safety, IPC-4101, and PCB substrate use.FR4 ComparisonsFR4 compared to G10, G11, cotton phenolic, and halogen-free laminates: flame retardancy, Tg, dielectric strength, CTI, machinability, and cost side-by-side.FR4 Properties & DatasheetFR4 properties datasheet: dielectric strength (~500 V/mil), Tg (130–170°C+), CTI, tensile, flexural, thermal, and electrical data for standard and high-Tg FR4.